- M31) Biggest is Andromeda (Sb. On Galaxy Evolution Lane. Large & Small Magellanic Clouds. ASTR 1040 Accel Astro: Stars & Galaxies

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1 ASTR 1040 Accel Astro: Stars & Galaxies Prof. Juri Toomre TA: Nicholas Nelson Lecture 24 Thur 7 Apr 2011 zeus.colorado.edu/astr1040-toomre toomre Stefan s Quintet On Galaxy Evolution Lane Look at our local group of galaxies Challenge of measuring distances in universe Most striking: many galaxies experience collisions thus becoming interacting galaxies Begin to discuss active galaxies and quasars Re-read 21.3 Quasars and active galactic nuclei in detail Our local group of galaxies 3 spirals: Andromeda (M31) Milky Way Triangulum (M33) 2 irregulars: LMC SMC 16+ dwarfs Biggest is Andromeda (Sb - M31) Andromeda is ~2.5 million light years away (or ~30 MW diameters), has ~1.5 mass of MW We see her as she was 2.5 million years ago, not as she is today! this is lookback time Oops! she may crash into MW in about 2 billion years Triangulum (M33) Large & Small Magellanic Clouds 1/5 mass of MW, spiral classified as Sc Several bright (pink) star forming regions LMC SMC 1

2 LMC has 30 Doradus,, home of SN 1987A SN 1987a before and after Clicker -- reading on galaxies How might you classify this galaxy? A. Sa B. SBb C. E D. SO B. Hubble: next showed universe appeared to be expanding! Vesto Slipher (1912) reported that most galaxies showed Doppler redshifts Edwin Hubble,, using new 100 telescope, started busily measuring galaxy redshifts Hubble (1929) announced that redshifts of galaxies appear to increase with distance from us This was startling: suggests an EXPANDING UNIVERSE! Hubble and recession of galaxies: measured many redshifts Further away, greater redshift! Hubble guessed their distances by size and brightness -- underestimated by factor 10! Hubble s s Law Hubble s s (1929) original Scatter here from random velocities of nearby galaxies, unreliable distance estimates 2

3 Best current values for expansion H o = 71 +/- 4 km/s/mpc velocity Universe expands like raisin bread! HUBBLE CONSTANT distance Hubble (1929) plot extended only to 2 Mpc,, H o was ~500! On an expanding balloon, no galaxy is at the center of expansion; no edge Expansion happens into a higher dimension (2-D surface into a 3-D 3 space) Is our 3-D 3 D space expanding through a 4 th dimension? Balloon analogy for expanding universe Mapping the universe: need distances to galaxies! Identify (and calibrate) properties of galaxies that could serve as STANDARD CANDLES -- beyond direct measure by trigonometric parallax 1. Make some measure of an object which identifies its luminosity (like period in Cepheid) 2. Use this luminosity and measure apparent brightness to infer distance to it ESTIMATE 1 Start with cluster A (upper) whose distance known via parallax Main-Sequence Fitting A M-S S Fitting pinned to nearby M45, Hyades Cluster,151 ly away Compare with other cluster B (lower) B Get distance to B from brightness difference 3

4 ESTIMATE 2 Cepheid variable stars ESTIMATE 2 Cepheids variables as standard candles Period - Luminosity relation brighter Cepheids have longer periods 1. Measure period of variability 2. From period- luminosity relation, infer the luminosity 3. Compare with apparent brightness and thus determine distance Cepheid variable in M100 (HST) Number of Fuzzier Distance Estimators A. Apparent brightness of (resolved) red and blue supergiants B. Size and brightness of H II regions (emission nebulae) or starbirth regions C. Intercompare distances so deduced for specific galaxies (overlapping rungs in `distance ladder ) Clicker: halo stars C. Massive O-type O stars are not found in the galactic halo because they are: A. too massive to be kicked into the halo from the disk B. so massive that they settle into the thinner disk C. too short-lived to have persisted from halo formation until today D. too far away for us to see them Why no O-stars? O C. Too short lived to be in the halo Distance ladder to measure universe Halo stars were born billions of years ago; the most massive stars don t t live nearly that long Will have disappeared by now (after having enriched the proto-galaxy gas with heavy elements) Different standard candles are useful for different distances 4

5 Measuring big distances to galaxies STANDARD CANDLES -- important ones in `distance ladder,, or `chain 1. Main-sequence fitting 2. Cepheid variables 3. Tully-Fisher relation 4. White dwarf supernovae Brightness ~ Luminosity / (Distance) 2 ESTIMATE 3 Fast rotation speeds in spiral galaxies more mass in galaxy higher luminosity Measure rotation speeds to infer luminosity Need bright edge-on spirals, estimate tilt Tully-Fisher Relation ESTIMATE 4 Standard explosion = fusion of 1.4 solar masses of material Even brighter: White dwarf supernovae Bright enough to be seen halfway across observable universe Nearly the same amount of energy released Useful for mapping the universe to the largest distances Supernovae in very distant galaxies Practical difficulty: White dwarf SN Need to catch them within a day or two of the explosion BEFORE About 1 per galaxy per century Need to monitor thousands of galaxies to catch a few per year galaxy clusters are useful 5

6 White dwarf supernovae Carbon fusion explosion: : mass transfer in binary takes white dwarf `over the edge Roughly same amount of energy released (calibrate) ESTIMATE 4 brighter SN dim more slowly! Distance ladder Overlapping standard candles calibrated DEMO REVIEW VELOCITY = H o x recession velocity ESTIMATE 5 Use Hubble s s Law itself to estimate vast distances D Measure velocity,, then: D = v / H o HUBBLE CONSTANT H o = 71 +/- 4 km / sec / Mpc distance Example: using H o = 70 km/sec/mpc Mpc, and finding that v = 700 km/sec D = 700 km/sec / 70 km/sec/mpc = 10 Mpc = 32 million light years Use Hubble s s Law for distances Measuring distances to remote galaxies is difficult, but measuring Doppler shifts (velocities) is easier from spectra Use Hubble s s Law to estimate biggest distances (really LOOKBACK TIME)! REFERENCE DISTANT GALAXY Knowing distances reveals large-scale galaxy clustering Find clusters + super-clusters : sheets and voids like `bubble bath 6

7 Telescopes are lookback time machines Lookback time (in expanding universe) Say it takes 400 million years for light to get from galaxy A to us in Milky Way TIME Yet during travel in spacetime,, both A and MW have changed positions by expansion MW A Today, we see Andromeda as she was 2.5 M years ago! Thus distance is a fuzzy concept LOOKBACK TIME is better 7